Microdisplay projection systems typically employ a transmissive or a reflective microdisplay imager, commonly referred to as a light valve or light valve array, which imposes an image on an illumination light beam. One of the important advantages on reflective light valves over transmissive light valves is that reflective light valves permit controlling circuitry to be placed in situ behind the reflective surface, and more advanced integrated circuit technology is available because the substrate materials are not limited by their opaqueness.
A reflective liquid-crystal-on-silicon (LCOS) imager is a kind of reflective microdisplay imager, which rotates and modulates the polarization state of incident light. Thus, polarized light is either reflected by the LCOS imager with its polarization state substantially unmodified, or with a degree of polarization rotation imparted to provide a desired grey scale. Accordingly, a polarized light beam is generally used as the input beam for reflective LCOS imagers, while a polarizing beam-splitter (PBS) is typically employed for splitting the incoming light beam into two polarized light beams in orthogonal polarization states.
Widely used for various portable and handheld projection display applications, a typical single-imager projection engine assembly 500 employs one LCOS reflective polarization modulation imager 110 and one PBS assembly 200a in the simplest but most compact configuration, illustrated in FIG. 1. One of the most obvious drawbacks of this Cartesian optical projection engine single-imager projection engine assembly 500, consisting of the single PBS assembly 200a and the single reflective polarization modulation imager 110, is that only limited portion of illumination light 10 in one polarization state is used for illuminating the reflective polarization modulation imager 110 and therefore, after modulation and reflection by the reflective polarization modulation imager 110, total illumination projected through the projection lens system 300 onto a projection screen 390 is limited. As shown in FIG. 1 in the prior art, the illumination light 10 includes a first polarized illumination light 11 in a first polarization state 1 and a second polarized illumination light 12 in a second polarization state 2 which is orthogonal to the first polarization state 1. Only a main portion of the illumination light 10 in the first polarization state 1 can be utilized while the complimentary portion of the illumination light 10 in the other orthogonal second polarization state 2 is unused for illuminating the reflective polarization modulation imager 110. Similarly, Only the illumination light 10 in the second polarization state 2 can be utilized while the illumination light 10 in the first polarization state 1 can not be utilized. Therefore, a conventional projection engine assembly has low light utilization